Hitia 17- Alternative Mast Construction

Comment by paul anderson on July 13, 2012 at 11:44am

wow,those are some pretty fine tolerances.

Comment by Omar M. Rashash on July 13, 2012 at 12:44pm

This might be a case where the rough surface left by a saw blade might be better.  My only concern at this point is that the joints, while perfect for resorcinal glue, may in fact be too tight for epoxy.  The danger exists that too much epoxy may be squeezed out under clamping pressure.  I may elect to go with plastic packaging wrap as my primary clamp.  It will permit me to still see the joint and selectively increase pressure where necessary.  An additional benefit is that it will not stick to the epoxy and will leave me a fairly flat surface from which to begin shaping.

I'll probably glue up my two foot test section, let it cure, and then test to failure.  This should tell me what kind of penetration the epoxy is giving me.  The epoxy glueup will consist of my usual unthickened epoxy followed by coating 1-2 hours later with epoxy thickened with cotton fibers.

Comment by paul anderson on July 13, 2012 at 11:55pm

give the joints a good sanding with a rough paper,believe me I have had the heartbreak of a dodgy mast glue failure due to high moisture/unseasoned timber heart break.Why not uses the rope method for clamping so you will not push out too much glue?

good luck, paul.

Comment by Omar M. Rashash on July 14, 2012 at 7:03am

Actually, sanding will NOT improve the characteristics of this particular glue joint.  This machine cut joint is second only to hand scrapped/planed in it's abillity to accept penetration of the adhesive.  Sanding will introduce material that will fill the pores in the wood, some of which will not be removed by wiping with the appropriate solvent.  This will reduce penetration of the adhesive and weaken the joint.

This is in direct contrast to sanding an epoxy sealed surface to "tooth" it and improve adhesion of the next coat, if the epoxy has gone beyond the ability to chemically bond to the next application.  Unless you know the wood is dry, the only way to avoid epoxy glue joint failure, due to the moisture content of the wood, is to use a moisture meter.  No amount of surface prep is going to help with epoxy if the wood is over 15% moisture content.

The rope method is one of the ways I'd to increase clamping pressure over the plastic wrap.  Large hose clamps, "c" clamp, and "f" clamps are others.

Comment by John PAUL Bould on July 16, 2012 at 8:24am

Looks very much like the mast for the 63 foot I helped James with back in the nineties!

Comment by Omar M. Rashash on July 16, 2012 at 9:15am

What some people think of as "new" is simply recycled from an earlier time.  Very little has changed in the art of wooden boat building in 2000 years.  One major change has been the Industriial Revolution, which gave us machine sawn timbers, machine cut screws, and plywood.  The other major change has been modern paints and adhesives, specifically Epoxy.  I do not consider fiberglass cloth to be as beneficial as most would think.

Comment by Georges Moutoussamy on July 19, 2012 at 2:14pm

A very good  job Omar. I thing that it is the better may to build a Wharram mast.

Comment by marc on July 22, 2012 at 12:50pm

Just to complete your work, here is some calculus :

percentage of emptiness in the mast (your work) 39.56% (JWD) 17.61% with epoxy fillets 30.54% without.

so this mast should be 22% lighter

percentage of wood to plane (your work) 11.93% (JWD) 19.80%

the thickness of wood after rounding is between 17 mm and 15 mm.

you have just to decide if do it clockwise or counterclockwise.

Comment by Omar M. Rashash on July 22, 2012 at 4:49pm

Thanks for the input Marc.  I've had calculus, through differential equations, but I promised myself I'd never do it in the real world.  It's always good when the math actually supports either the 'rule of thumb' or what your experience tells you should work.  The mast could be even lighter, if I was willing to go with the Douglas Fir coefficient of .15 (.525" instead of .7"), but I decided to not push my luck.

Comment by Hans Hammig on July 30, 2012 at 2:38pm

This is marvelous. I had similar ideas, but I was not able to solve the problems involved. Eventually I used sewerage pipes laminated with glass and epoxy (66 % to 34 %) and post cured. They are 100 mm diameter and weight about 4 kg per meter (9 m long).

Comment

• ‹ Previous
• 1
• 2
• Next ›
• Page